Device for connecting extreme low temperature cable with normal temperature electric apparatus

ABSTRACT

A disconnecting switch is provided in the connecting part between a cable kept at extremely low temperature by means of extremely low temperature coolant and an electric apparatus kept at normal room temperature such as a gas-filled duct transmission line, transformer etc., which disconnecting switch is opened when current is interrupted. And the disconnecting switch is housed in a vacuum casing.

United States Patent [1 Yoshioka et a1.

1451 Feb. 12, 1974 DEVICE FOR CONNECTING EXTREME [54] 3,47I,669 l/l969Curtis ZOO/144B X LOW TEMPERATURE AB E WIT NORMAL TEMPERATUCRE E SFOREIGN PATENTS OR APPLICATIONS 6,406,498 l2/l964 Netherlands ZOO/I63APPARATUS 1,032,364 6/1958 Germany 200/163 [75] Inventors: YoshioYoshioka; Kenichi Okuyama,

both of Hltach" Japan Primary Examiner.l. R. Scott [73] Assignee:Hitachi, Ltd., Tokyo, Japan Assistant Examiner-Robert A. Vanderhye F --CA t l' I Filed: Sept. 1972 Attorney, Agent, or zrm raig and 11 one] I 21A l. N 290,356 1 pp 0 2 [57 ABSTRACT [52] us CL U 200/163, l74/l5 BHI74/DIG. 6 A disconnecting switch is provided in the connecting 200/144part between a cable kept at extremely low tempera- 51 Int. Cl. HOlh31/32, H02g 15/22 by means of extremely temperature [58] Field of Search200/163, 144 B 166 C, 166 K; and an electric apparatus kept at normalroom tem- 174/l9 DIG 6 9 R BH peraturesuch as a gas-filled ducttransmission line; transformer etc., which disconnecting switch is [56]References Cited opened when current is interrupted. And the discon-UNITED STATES PATENTS necting switch is housed in a vacuum casing.3,539,702 11/1970 Edwards et a1 .1 174/15 BH X 9 Claims, 3 DrawingFigures v m q 27 S 1 37 l u W s 45 i PATEN-TED FEB I 2 i974 SHEET 2 OF 3DEVICE FOR CONNECTING EXTREME LOW TEMPERATURE CABLE WITH NORMALTEMPERATURE ELECTRIC APPARATUS BACKGROUND OF THE INVENTION 1. Field ofthe Invention The present invention relates to a device for connectingan extremely low temperature cable having conductor kept at extremelylow temperatures with an electric apparatus kept at normal roomtemperature such as a gas-insulated cable a transformer and a circuitbreaker, employing as insulating medium sulphur hexafluoride gas(hereafter referred to as SF gas) or oil. Here, the term extremely lowtemperatures refers to those temperatures at whichair composed mainly ofnitrogen, oxygen and hydrogen can be liquefied.

2. Description of the Prior Art The extreme low temperature cable iseither a cable in which conductors are refrigerated by such a liquidcoolant having a very low boiling point asliquid helium, nitrogen orhydrogen so that the specific resistances of the conductors may be byfar lower than at normal temperature so as to reduce heat loss, or acable in which such a superconductor as niobium, niobiumtitanium orniobium-tin cooled down to extremely low temperatures is used so thatthe conductor kept in the superconductive state and therefore havingzero resistance may provide no heat loss. It is now proposed that suchan extreme low temperature cable should be used as either transmissionlines for supplying huge electric energy for a big city or under-groundcables for drawing electric energy from a power station installed on thebeach to inland distribution systems.

If the conductor of the extreme low temperature cable is coupleddirectly to an electric apparatus kept at room temperature, then theinsulating medium used in the apparatus, which is in gaseous state atroom temperature, will be liquified or solidified, so that theinsulating property of the medium will be destroyed. For example, if anextreme low temperature cable with liquid nitrogen as refrigerant iscoupled directly to an electric apparatus with SF 6 gas as insulator,the SP gas is liquefied or solidified so that the insulating property ofthegas collapses. The reason is that since the conductor of the cable iskept at a temperature of about -l96C the connecting part of the electricapparatus and the SF gas near there is cooled down to temperatures byfar lower than 64C that is the boiling temperature of the SE, gas. It istherefore necessary for insulating medium or are extinguishing medium tobe prevented from being supercooled by providing moderate thermalgradient or several steps of different temperatures between thetemperature at which the extreme low temperature cable is maintained andthe temperatures at which the normal temperature electric apparatus maybe kept, that is, which are equal to or higher than the roomtemperature. Thus, the conventional way of connecting an extreme lowtemperature cable with a normal .temperature'electric apparatus,employed the provision of a plurality of intermediate coolant layersinserted between the coolant of the cable and the electric apparatus,whose temperatures increase gradually toward the apparatus. Even withsuch a means, however, which can only fulfill its function due to Jouleheat generated at the connected part when the cable is energized, thenormal temperature apparatus will be extremely cooled by the cablecoolant if current is interrupted, so that the supercooling of theapparatus results in the liquefication or solidification of theinsulating SF gas or oil and therefore the deterioration in dielectricstrength of the insulator. Moreover, in case of initial cooling of anextreme low temperature cable by filling the cable duct with a suitablecoolant, quite a long time is spent before the cable has reached thethermal equilibrium if the cable is long enough to be adapted forpractical use. And during the preequilibrium transient, a considerableamount of heat is transferred from the normal temperature electricapparatus to the extreme low temperature cable, and therefore theefficiency of initial refrigeration is much degraded.

SUMMARY OF THE INVENTION One object of the present invention is toprovide a device for connecting an extreme low temperature cable with anormal temperature electric apparatus, with which device the insulatingmedium of the normal temperature electric apparatus can be preventedfrom being liquefied or solidified by the coolant of the cable.

Another object of the present invention is to provide a device forconnecting an extreme low temperature cable with a normal temperatureelectric apparatus, with which device it is possible to minimize thetransfer of heat from the apparatus to the conductor of the cable.

An additional object of the present invention is to provide asimple-structured device for connecting an extreme low temperature-cablewith a normal temperature electric apparatus.

A yet another object of the present invention is to provide a device forconnecting an extreme low temperature cable with a normal temperatureelectric apparatus, with which the state of connection is notdeteriorated due to the thermal contraction of the cable conductor.

The present invention is, therefore, characterized in that in theconnection part between the cable conductor kept at extremely lowtemperature and an electric apparatus kept at nonnal temperature isprovided a disconnecting switch which is open while current isinterrupted and that the disconnecting switch is placed in or surrounderby vacuum or pressurized gas identical in substance with the liquidcoolant for the extreme low temperature cable, whereby not only theinsulator for the normal temperature electric apparatus can be preventedfrom being liquefied or solidified through super cooling due to the heattransfer to the cable conductor when current is interrupted, but alsothe liquid coolant for the cable can be prevented from being muchvaporized due to the heat transfer from the apparatus to the cable.

Further objects and features of the present invention will be moreapparent when the following lines of this specification which treat afew embodiments of the invention are read with the aid of the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top plan view of a deviceembodying the present invention, which connects an extreme lowtemperature cable with a gas-filled duct transmission line.

FIG. 2 is a cross sectional view of the device shown in FIG. 1.

FIG. 3 is a cross sectional view of a device as another embodiment ofthe present invention, which serves to connect an extreme lowtemperature cable with a gasfilled duct transmission line.

DESCRIPTION OF THE PREFERRED V EMBODIMENTS FIG. 1 shows the connectionpart between an extreme low temperature cable and a gas-filled ducttransmission line 11, in which the cable 10 and the line 11 areconnected'with each other via the end portion 12 of the cable 10 and adisconnecting switch 13 and in which the liquid coolant for the cable 10is recovered by means of a coolant collector 14 while gas generated as aresult of vaporization of the liquid coolant is retaken by means of agas collector 15.

The disconnecting switch 13 in the connection part is either opened orclosed by a manipulator 16.

Referring to FIG. 2 which shows the cross section of the connection partshown in FIG. 1, the cable 10 comprises a hollow cable conductor 21, anelectrical insulator 22 covering the conductor 21 and a thermalinsulator 23 spaced from the electrical insulator 22. The thermalinsulator 23 is a multi-lamination of thermal insulating material andthin aluminum sheet as heat reflector and the multi-laminationconstitutes a vacuum-tight duct to realize super-insulation. A liquidcoolant 24 such as liquid nitrogen, liquid hydrogen or liquid helium isintroduced into the hollow of the cable conductor 21 so as to keep thetemperature of the conductor 21 extremely low. The cable conductor 21 ispreferably made of Cu or Al whose electric resistance is considerablylowered at extremely low temperature or made of a superconductor such asNb, NbTi or Nb Sn the electric resistance of which is reduced to nearZero when it is cooled down below a critical temperature.

The gas-filled duct transmission line 11 comprises a conductor 25, acasing 26 and a spacer 27 and SF gas as insulating medium fills thespace 28 defined by the casing 26 and the conductor 25. The connectionpart constituted of the end portion 12 of the cable 10 and the circuitbreaker 13 comprises a connecting conductor 29 having a hollow intowhich the liquid coolant 24 for the cable 10 is also introduced toprovide a temperature gradient from normal to extremely lowtemperatures, an insulating support 30 for thermally and electricallyinsulating and supporting the connecting conductor 29, and a contactor32 detachably engaged with a connector member 31 'of the connectingconductor 29 and slidably engaged with the conductor 25 of thegas-filled duct transmission line 11. One end of the contactor 32 istipped with a finger member 33 and the other end of the contactor 32 isconnected via a manipulating rod 34 of electrically insulating materialwith an external manipulating rod 35. Moreover, the contactor 32 is notonly insulated but also supported by a spacer 36.

In the sliding part in which the conductor 25 of the gasfilled duct line11 and the contactor 32 are contacted slidably with each other, acollector 42 fixed to the conductor 25 is in slidable contact with thecontactor 32. A spring 43 urges the collector 42 against the contactor32 and a shielding member 44 covers the spring 43. The finger member 33is also provided with a spring 45 to produce a pressing force.

Now, the gas generated from the liquid coolant 24,

1 which established temperature gradient by cooling the connectingconductor 29, is gathered into the external gas collector 15 through agas outlet port 37 made of insulating material. The gas outlet port 37is surrounded by a thermal insulator 46 and the thermal insulator 46 isin turn covered by a sheath 47.

The gas collected in the gas collector 15 is cooled again to be used asliquid coolant for the cable 10. The end portion 12 of the cable 10 anda part of the disconnecting switch 13 are housed in a casing 38, whichis evacuated to create vacuum therein. And in order to maintain thevacuum condition, bellows 39 are provided between the casing 38 and theexternal manipulating rod 35 and the spacer 27 for the gas-filled ductline 11 also hermetically seals the casing 26. A flange member 40 isprovided between the extreme low temperature cable 10 and the casing 38of the end portion to hermetically seal the casing 38.

The liquid coolant 24, after having cooled the cable conductor 10 ispoured out of a coolant outlet port 41 into the coolant collector 14 andrecooled to be used for cooling the cable again. 7

FIG. 2 shows the state of the device in which current is drawn throughthe connecting part, that is, current is flowing from the conductor 21of the cable 10, through the connecting conductor 29, the connectormember 31, the finger member 33, the contactor 32 and the collector 42,to the conductor 25 of the line 11. In this state, a small part ofliquid coolant 24 flows into the connecting conductor 29 and heatexchange takes place at the indentations formed on the connectingconductor 29 so that the liquid coolant 24 is vaporized and warmedgradually to establish in the connecting conductor 29 a temperaturegradient from extremely low to normal temperatures. By virtue of thistemperature gradient, the liquefication or solidification of the SP gasdue to the supercooling of the gas-filled duct transmission line 11,i.e.; the deterioration in the dielectric strength of the gas, isprevented. In addition, the evaporation of the liquid coolant 24 due tothe heat transfer from the line 11 to the cable 10 is prevented.

On the other hand, in case where current is not drawn or where the cableis initially cooled, the external manipulating rod 35 is shifted to theleft by means of the manipulator 16 to disengage the contactor 32 fromthe connector member 31. Under such a condition, the temperature at theconnector member 31 of the connecting conductor 29 is much lower thannormal temperature since no current is drawn through the conductor 29,that is, no Joule heat is generated therein, but the space surroundingthe connector member 31 is vacuum and therefore thermally insulating sothat the SE; gas filling the space 28 of the gas-filled duct line 11 isnever supercolled. Moreover, with this disconnecting switch means, heattransfer from the line 11 to the cable 10 never takes place so that theliquid coolant can be efficiently introduced into the cable conductor 21at the initial cooling of the cable conductor 21. The contactor 32 isprovided on the gas-filled duct transmission line and operated by theexternal manipulating rod 16, which is formed of a thermal insulatingmaterial so that thermal transmission through the external manipulatingrod 16 to the extremely low temperature cable 10 is prevented. If thecontactor 32 is brought into contact with the connector member 31 inadvance of current conduction after the cooling of the cable 10 iscompleted, then transient heat transfer from the contactor 32 to theconnector member 31 takes place and the contactor 32 begins to becooled. However, if current is drawn in a short moment, the steadystatecurrent conduction is established before the temperature of theconductor 25 of the line 11 is lowered to excess and therefore theinsulating property of the SP gas is deteriorated.

FIG. 3 shows another embodiment of the present invention. In FIG. 3,there is illustrated an extreme low temperature cable 50 comprising ahollow cable conductor 61, an electrical insulator 62 covering the cableconductor 61 and a thermal insulator 63 coated on the electricalinsulator 62, the hollow of the cable conductor 61 being filled withliquid coolant 64 which cools the conductor down to extremely lowtemperature.

A gas-filled duct transmission line 51, on the other hand, comprises aconductor 65, a casing 66 and a spacer 67, and the internal space 68 isfilled with SF gas as insulator. The end portion 52 of the cable 50 ishoused in a casing 69 which defines a closed space 88 with the cable 50and provided with a coolant outlet port 70 of the insulating materialfor letting out the liquid coolant 64, which port 70 is covered outsidethe casing 69 with a thermal insulator 71.

A disconnecting switch 53 comprises a movable contactor 73 detachablyengaged with a fixed contactor 72 formed at the end of the cableconductor 61 and a connecting rod 74 supporting the movable contact 73at its one end and engaged slidably with the conductor 65 at the otherend, the connecting rod 74 being at the other end connected rigidly withthe manipulating rod 75 of electrically insulating material. Theslidable contact between the conductor 65 of the gas-filled duct line 51and the connecting rod 74 is maintained by means of a collector 76 fixedto the conductor 65 and kept in slidable contact with the rod 74. Aspring 77 urges the collector 76 against the rod so as to establish astable contact between the collector 76 and the rod 74. A shield member78 covers the collector 76. The movable contactor 73 comprises acontacting piece 79, a spring 80 for applying urging force to thecontacting piece 79 and a shield member 81 covering the spring 80. Thesecomponents constituting the disconnecting switch 53 is housed in acasing 82. The end of the cable conductor 61 is supported in place by aspacer 83 fixed to the easing 82 and the collector 76 is supportedrigidly by a spacer 84 fixed to the casing 82. The manipulating rod 75is connected via link lever 85 with an external manipulating rod 86. Thespace 87 within the casing 82 is vacuum. Therefore, a hermetical sealingis provided between the casing 82 and the link lever 85 and the spacer67 for the duct line 51 also hermetical seals the duct casing 66 andtherefore the casing 82. The space within the casing 69 for the endportion 52 of the extreme low temperature cable 50 is also vacuum.

FIG. 3 shows the state of the disconnecting switch in which current isflowing from the cable conductor 61 of the extreme low temperature cable50, through the fixed contactor 72, the movable contactor 73, theconnecting rod 74 and the collector 76, to the conductor 65 of thegas-filled duct transmission line 51. In this state, a temperaturegradient from extremely low to normal temperatures is establishedbetween the cable 50 and the gas-filled duct line 51 due to Joule heatgenerated in the conducting part between the conductors 6 percooling ofthe conductor of the gas-filled duct line 51 with the result that thedielectric strength of the SP gas is degraded, and that heat istransferred to the conductor 61 of the cable 50 to vaporize the liquidcoolant 64 too much.

If, on the other hand, no current is drawn through the connecting part,the external manipulating rod 86 is actuated downward by means of amanipulator (not shown). Accordingly, the connecting rod 74 is shiftedupward through the associated movement of the link lever 85 and theinsulating manipulating rod so that the movable contactor 73 isdisengaged from the fixed contactor 72..Then, thermal insulation isestablished between the movable and the fixed contactors 73 and 72 sinceboth the contactors are placed in vacuum. Consequently, it never happensthat the SP gas of the internal space 68 of the gas-filled duct line 51is supercooled and that heat transfer from the gas-filled ducttransmission line 51 to the extreme low temperature cable 50 takesplace.

In the embodiment shown in FIG. 3, there is provided no special meansfor creating a temperature gradient such as the indentations of theconnecting conductor 29 in the embodiment shown in FIG. 2, but thissimplified device can also establish a suitable temperature gradientbetween the extreme low temperature cable 50 and the gas-filled ducttransmission line 51 if liquid nitrogen, the temperature of which isrelatively higher, is used as coolant.

In each of the above described embodiments, the internal space of theconnecting part is kept vacuum, but a pressurized gas of helium,hydrogen or neon may be introduced instead into the space. In such acase, however, electrical and thermal insulation property is lessimproved than in case where the space is vacuum. And, in order to obtaininsulation to the same degree as in vacuum, the size of the casing andtherefore the volume of the insulating gas must be increased. However,in case where liquid nitrogen is used as coolant for the extreme lowtemperature cable, the transfer of heat enough to liquefy the insulatingmedium such as SF gas is prevented even if pressurized helium, hydrogenor neon gas, which is not liquefied at the temperature or liquidnitrogen, is introduced in the space of the connecting part.

We claim:

1. A device for connecting an extremely low temperature cable with anoraml temperature electrical apparatus; said extremely low temperaturecable consisting of a first conductor, an electrical insulating meansprovided around said first conductor, a thermal insulating meansprovided around said electrical insulating means and a liquid coolantkept at extremely low temperature and in contact with said conductor;and said normal temperature electric apparatus consisting of a secondconductor, a first casing housing said second conductor therein andspaced from said second conductor and an electrical insulating mediumcontained in said casing; said device comprising I means for forming atemperature gradient from an extremely low temperature to a normaltemperature including a connecting conductor for connecting said firstconductor with said second conductor;

a second casing provided between said thermal insulating means and saidfirst casing and housing said connecting conductor therein, said secondcasing being spaced from said connecting conductor and electricallyinsulated therefrom;

spacer means for hermetically sealing said second casing from said cableand said electric apparatus and a disconnecting switch including atleast a pair of contactors provided in said second casing between a partof said connecting conductor and said second conductor, one of saidcontactors being movable so that said contactors may be separated fromeach other when current is to be interrupted so as to cut off thermalconduction through said connecting conductor.

2. A device according to claim 1, wherein the space formed within saidsecond casing between said cable and said apparatus is vacuum.

3. A device according to claim 1, wherein the space formed in saidsecond casing between said cable and said apparatus is filled with apressurized gas having a liquefication temperature lower than that ofsaid coolant.

4. A device according to claim 1, wherein said contactors comprise afixed contact provided on said cable side and a movable contact providedon said apparatus side and movable to contact with said fixed contact.

5. A device according to claim 1, wherein said contactors are mounted topermit said first conductor to slide in the axial direction thereof andto compensate for the change of the length in the axial direction ofsaid first conductor due to thermal expansion and contraction thereof.

6. A device according to claim 1, wherein said connecting conductor isprovided with means for introducing therein vaporized gas derived fromsaid liquid coolant to create in said connecting conductor a temperaturegradient from near normal temperature to an extremely low temperature'7. A device according to claim 1, wherein said normal temperatureelectrical apparatus is a gas-filled duct transmission line having aspacer fixed to said first casing and supporting said second conductorin the center thereof and SP gas contained in said first casing.

8. A device according to claim 1, wherein said connecting conductor is asubstantially linear extension of said first conductor, said one of saidcontactors including an elongated conductor bar disposed transversely tosaid connecting conductor to which the other contactor is connected,said elongated conductor bar being in sliding contact with said secondconductor.

9. A device according to claim 1, wherein said connecting conductor is asubstantially linear extension of said first conductor, said one of saidcontactors including an elongated conductor bar disposed transversely toand insulating contact with said second conductor.

1. A device for connecting an extremely low temperature cable with anoraml temperature electrical apparatus; said extremely low temperaturecable consisting of a first conductor, an electrical insulating meansprovided around said first conductor, a thermal insulating meansprovided around said electrical insulating means and a liquid coolantkept at extremely low temperature and in contact with said conductor;and said normal temperature electric apparatus consisting of a secondconductor, a first casing housing said second conductor therein andspaced from said second conductor and an electrical insulating mediumcontained in said casing; said device comprising means for forming atemperature gradient from an extremely low temperature to a normaltemperature including a connecting conductor for connecting said firstconductor with said second conductor; a second casing provided betweensaid thermal insulating means and said first casing and housing saidconnecting conductor therein, said second casing being spaced from saidconnecting conductor and electrically insulated therefrom; spacer meansfor hermetically sealing said second casing from said cable and saidelectric apparatus and a disconnecting switch including at least a pairof contactors provided in said second casing between a part of saidconnecting conductor and said second conductor, one of said contactorsbeing movable so that said contactors may be separated from each otherwhen current is to be interrupted so as to cut off thermal conductionthrough said connecting conductor.
 2. A device according to claim 1,wherein the space formed within said second casing between said cableand said apparatus is vacuum.
 3. A device according to claim 1, whereinthe space formed in said second casing between said cable and saidapparatus is filled with a pressurized gas having a liqueficationtemperature lower than that of said coolant.
 4. A device according toclaim 1, wherein said contactors comprise a fixed contact provided onsaid cable side and a movable contact provided on said apparatus sideand movable to contact with said fixed contact.
 5. A device according toclaim 1, wherein said contactors are mounted to permit said firstconductor to slide in the axial direction thereof and to compensate forthe change of the length in the axial direction of said first conductordue to thermal expansion and contraction thereof.
 6. A device accordingto claim 1, wherein said connecting conductor is provided with means forintroducing therein vaporized gas derived from said liquid coolant tocreate in said connecting conductor a temperature gradient from nearnormal temperature to an extremely low temperature.
 7. A deviceaccording to claim 1, wherein said normal temperature electricalapparatus is a gas-filled duct transmission line having a spacer fixedto said first casing and supporting said second conductor in the centerthereof and SF6 gas contained in said first casing.
 8. A deviceaccording to claim 1, wherein said connecting conductor is asubstantially linear extension of said first conductor, said one of saidcontactors including an elongated conductor bar disposed transversely tosaid connecting conductor to which the other contactor is connected,said elongated conductor bar being in sliding contact with said secondconductor.
 9. A device according to claim 1, wherein said connectingconductor is a substantially linear extension of said first conductor,said one of said contactors including an elongated conductOr bardisposed transversely to and insulating contact with said secondconductor.